This invention relates to a multiple-speed electromagnetic clutch with a belt drive that is mounted on an engine crankshaft to drive multiple rotary devices.
One device that might be driven by such a clutch is a turbocharger.
Many techniques have been devised to increase the performance of automotive internal combustion engines. Supercharger and turbocharger systems have been developed that substantially boost engine performance. These systems operate to increase air pressure delivered to the intake manifold of the engine before being mixed with the fuel. The increased air pressure enhances the combustibility of the fuel, thus making it more powerful. This added power then increases engine power and torque at both lower and higher rpms than would otherwise be possible. Turbo chargers are simple and cheap, unlike superchargers that do not suffer from a response lag time because they are generally mechanically driven. Superchargers are more complicated and can be very expensive, although they do solve the problem of incomplete combustion when an engine is initially leaving idle speeds. Acceleration is also greatly improved with a typical mechanically driven supercharger.
However, the complicated belts and pulleys used in mechanical superchargers require for operation as much as 40% of the engine's power output, which exacts a price of shortening the engine's life span for the increased performance.
Turbochargers, on the other hand, are passive performance boosting devices that are driven by the exhaust from the engine. The passive design of the turbocharger does not adversely affect the life span of the engine to the degree that a supercharger does.
Turbochargers suffer a lag in response time because they are driven by exhaust gases and these gases are under very little pressure and velocity when the engine is at idle. The turbocharger has very little rotational velocity to supply the engine with all the fresh air that is needed to complete combustion of all the fuel that is being forced into a vehicles combustion chamber. Hence large Semi's, ships, tractors, trucks, power plants and transit buses can be seen emitting black smoke as the diesel fuel is not completely burned initially on some heavy vehicles.
The turbo chargers have not gotten over their initial lag before they offer a power boost to the engine.
Even cars are being equipped more frequently with turbo chargers as engine size and weight must be kept to a minimum but the driving public wants more power from these smaller engines. These automobiles will suffer from the same incomplete combustion as larger vehicles although it will be less obvious from a visual point of view and surely less time in duration, but incomplete combustion none the less.
To overcome this some areas of the country are requiring oxygenated fuels, and low-sulfur diesel, be burnt in all of their vehicles especially during certain times of the year. Auto manufacturers are also to begin producing 85 compliant motors for vehicles. In essence, these vehicles can burn a mixture of 85 per cent ethanol and 15 per cent gasoline. This extra oxygen improves the initial lack of oxygen some vehicles suffer from on acceleration from low speeds or stopped conditions thereby reducing pollutants and smog contributing effects. If these engines were to be adjusted lean enough (oxygen rich-fuel stingy), for all operating conditions they would overheat during highway conditions on warm days. They can be adjusted and controlled to burn completely at cruising speeds but that leaves an oxygen-deprived state at idle.
Smaller engines in personal vehicles would be possible and acceptable to the consuming public if there was a way to turbocharge these vehicles without the hassle that comes with present turbochargers. This hassle is the warm-up period before a car is driven at highway speeds and a cooling-off period before the engine is shut off.
Presently, catalytic converters aid in the low emissions scenario of most gasoline powered engines, but these only work after they have become hot, and are little or no help to a cleaner burning engine when the engine is first started up, and before it is warmed up.
Another problem with ordinary turbochargers is that heat of the exhaust gases which drive the turbocharger is transferred to the center bearing that provides support for the turbocharger's turbine. Present designs typically have an oil supply and engine coolant supply going to the turbocharger bearing. This is to maintain lubrication and cooling to this critical bearing while the engine is running. This design is adequate as long as the engine is operating. However, when the engine is shut off the oil and coolant stop flowing immediately and if the bearing is supporting a hot turbine that has just been revolving at 40,000 rpm's or more the bearing literally begins to cook.
Most recommendations are for allowing the motor to idle 3 minutes before shutting off the engine. This allows this bearing to cool off before removing critical oil and cooling from the bearing. Repeated occurrences of shutting off the engine before allowing an adequate cooling-off time for the turbocharger bearing leads to premature bearing failure and expensive repairs.
Several solutions have been developed to overcome the problem of turbo lag. One solution combines a supercharger with a turbocharger. The supercharger drives the turbocharger until the engine has reached a threshold level at which point it takes over the supercharger's job. This has the advantage of limiting the use of the supercharger, but it also has the drawback of being an active system that shortens engine life, as well as being overly complex.
By driving a simple turbocharger by a belt, and keeping it simple and inexpensive, the best of both can be achieved. By removing the turbine from exhaust gas stream, the excess heating to the turbine bearing is minimized and the compressed air itself is the only factor for heating. However, this heat transfers minimally to the bearing. The bearing is thus able to better withstand possible abuse by the average driver who doesn't want to be bothered by details, such as letting the engine run for several minutes after they reach their destination.
One simple yet effective way of driving a turbocharger with a belt is to place a multiple-speed electromagnetic clutch on the engine crankshaft and drive the turbocharger from a belt attached to the clutch.
By placing the clutch on the crankshaft rather than on the specific rotary device to be driven, the crankshaft can drive multiple rotary devices, in addition to a turbocharger, such as alternators, generators, air conditioners, fans, etc.
Two-speed electromagnetic clutches for driving a single engine rotary device are known, as shown by U.S. Pat. No. 3,675,747. However, there are a number of disadvantages with these devices.
First, these devices attach directly to the rotary device to be driven, rather than to the engine crankshaft. Therefore, they are only capable of driving a single rotary device. In order to drive multiple rotary devices at different speeds, multiple clutches must be used, with a clutch per rotary device to be driven and corresponding additional belts between each clutch and the crankshaft.
Second, these devices are constructed with components only of sufficient size to drive a single device, because that is the intent. They are not robust enough to drive multiple devices, even if some way was found to do so. For example, the '747 patent operates by having the electromagnet move to alternate clutch plates, rather than having the clutch plates move to the electromagnet. By having the magnet move instead of the clutch plate, this device limits the amount of power that can be transmitted through the pulleys because layered torsion springs can not be added in heavy-duty applications. Also, when the magnet moves over to engage the clutch plate, the electric windings about the magnet will be compromised in short order and wires will be worn through and electrical continuity will be lost because it is the face of the magnet coming into contact with the clutch plate that is doing all of the holding. In a conventional electromagnet, the electromagnet is in a fixed position laterally with respect to the shaft and a casing is around the magnet. This will protect the magnet's facing.
Thirdly, any of these devices that mount to the driven device could not be used with a device such as an alternator or generator, because the magnetic field of the electromagnet would conflict with the magnetic fields present about such devices. These devices are therefore limited to non-electromagnetic rotary devices such as fans or air conditioner pumps.
It is the object of the present invention to overcome the above-listed disadvantages of earlier two-speed electromagnetic clutches.